Boiler tubes are generally arranged in large panels or banks of parallel tubes that are connected together with a metal membrane. In some cases a weld overlay comprising a metal or alloy is placed on portions of the tube bank in an effort to prevent corrosion.
Because of corrosion, boiler tubes occasionally require replacement. Ordinarily, replacement of tubes involves cutting and removal of relatively large sections of the existing panel of tubes and replacement with a new panel of tubes.
The section of the panel of tubes that is to be replaced is generally cut out using a power saw or a cutting torch. After the section that is to be replaced has been removed, it is necessary properly to prepare the tube ends of the remaining panel of tubes exposed by the removal of the section. Preparation of the tube ends requires beveling of the tube ends to facilitate a good weld. To facilitate efficient beveling of the tube ends, it is highly desirable to remove a portion of the membrane and weld overlay between each pair of exposed tube ends. It is also desirable to remove any film from the tube ends. In addition, there are other circumstances in which various materials must be removed from a tube end.
The prior art contains milling heads that perform one or more of the membrane, weld overlay and film removal steps. For example, such a milling head is disclosed in U.S. Pat. No. 6,955,507, incorporated herein by reference.
However, the cutting blades, and the means to secure them to the milling heads, of the prior art are susceptible to breaking. Moreover, the cutting blades are generally secured to the milling heads of the prior art by screws. When such a screw breaks, a portion of the screw is left in the hole in which it was threaded. It is difficult and time consuming to extract this portion of the screw from the threaded hole so that a replacement blade may be secured to the milling head by another screw. It is, therefore, an object of the present invention to provide a tube end milling head with cutting means that are less susceptible to breaking and that can be replaced quickly and efficiently in the event that they do break.